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The llluminometer Pod 


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build, hack, tweak, share, discover, J 


uminometer Pod 

Written By: Marc Barbani 


• Needlenose pliers (1) 

• Soldering iron (1) 

• Wire cutters (1) 
aka side cutters 

• Wire strippers (1) 


• Solar cell (1) 

the kind found in solar garden pathway 

5- minute epoxy (1) 

Meter (1) 

Potentiometer (1) 

iPod case (1) 



In trying to determine which was the better of two LED spotlights for reading in my easy 
chair, I had the need for a quick and simple light meter that could tell me which of the two 
different brands of bulbs I had would put out the the best light from a small recessed fixture 
on my ceiling. They were both rated at 3 watts, each comprised of 3 individual 1-watt LEDs 
built into a standard base. Even though they were the same wattage, their light output just 
seemed different. With that, I gutted my defective iPod and kept the metal case. I removed 
the solar cell from one of those ridiculous solar garden lights, stole a VU meter from a 
1970's-era cassette tape deck (remember those?), and removed a small variable resistor 
from a discarded monitor circuit board. I put these 4 parts all together and created the 

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The llluminometer Pod 


uminometer Pod." 

A light meter in its most basic form, the llluminometer Pod gives a relative indication of light 
source intensity, not an actual measure of lumen output. This is what I wanted, a simple light 
meter that would give different meter needle indications from various light sources at a given 
distance from the source. By placing the unit directly under a light source and adjusting the 
variable resistor to a set marker on the meter dial, I could try different light bulbs and the 
meter needle would rise or fall accordingly with different light intensities. Amazingly, it can 
measure subtle differences in similar light sources that are barely perceptible to the human 

Start by completely removing the 
innards of an iPod that gave up the 
ghost. Remove the plastic end 
caps and everything will eventually 
slide out, leaving a nice flat ovular 
aluminum canister. 

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The llluminometer Pod 

• Remove the solar cell from a solar 
garden light by carefully prying it 
loose from the globs of silicone 
holding it in place in its top end. 
These "lights" barely illuminate 
anything more than their own 
lenses, let alone a pathway, but 
they are now excellent and 
inexpensive sources of solar cells, 
NiCad batteries, photocells, and 

• The solar cell is delicate and its 
wires can come off if not handled 
carefully. Put a blob of epoxy on 
the back to hold the wires in place. 
If they get accidentally pulled off, 
there is no putting them back on, 
rendering the cell useless. 

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The llluminometer Pod 

• Find an old meter and a pot. The 
meter shown is a 0-1 mA VU meter 
originally used to indicate audio 
levels from a vintage cassette 
deck. Its graduations were perfect 
for this use and it fit nicely into the 
large circular hole of the iPod case. 
But any small meter will work. 

• I made a spacer out of 1/16" PVC 
sheet and epoxied it to the back of 
the meter. This raised it up enough 
to keep its terminals from 
contacting the metal case, which 
was a little too shallow for the 
depth of the meter. 

• The pot came from an old monitor's 
circuit board. Its value is 100k 
ohms, but a 50k ohm will work OK 

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The llluminometer Pod 

• It fits near-perfectly under the clear 
window of the iPod case. Use a few 
blobs of epoxy to hold it in place. 

Connect them all together by 
soldering the positive (red) wire of 
the solar cell to one end terminal of 
the potentiometer, and another wire 
from the middle and other end 
terminal together to the "+" (plus) 
terminal of the meter. Then solder 
the negative (black) wire of the 
solar cell to the "-" (minus) 
terminal of the meter. 

Put heat-shrink tubing or electrical 
tape on the meter terminals to keep 
them from accidentally shorting to 
the back of the metal iPod case. 

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The llluminometer Pod 

• At this point the meter will actually 
be working as there is no power 
switch, so make sure the pot is 
turned all the way to its maximum 
setting to avoid damaging the 
meter from any light source you 
are working under. Epoxy the 
meter to the case and wedge the 
potentiometer in the bottom slot 
and put a dab of epoxy to secure it. 

Now go try it out on different 
sources of light and see how the 
meter needle responds. If you take 
it outside, avoid direct sunlight as 
old Sol is very powerful and can 
peg the meter needle quite easily! 

This document was last generated on 201 2-1 1 -02 1 1 :53:30 PM. 

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